Various efforts in neuroscience are directed towards determining whether neural activity in a specific brain region, or in a set of genetically-identified neurons, contributes to a particular neural computation, behavior, or neurological or psychiatric disorder. For centuries, insights have come from studies of human patients with specific lesions, as exemplified by Paul Broca's delineation in the 1860s of the eponymous brain area that, when dysfunctional, results in deficits of speech production. Many studies have used ablation or pharmacological shutdown of neurons or brain regions in animals, or careful analysis of patients, to parse out the physical substrates of normal and abnormal behavior. However, growing awareness that activity in multiple brain regions may be coordinated during performance of a behavior, or in a particular neural dysfunction, has raised the question of precisely when specific brain regions or neurons contribute. For example, a large number of in vivo recording studies have demonstrated, for many brain regions, that specific neurons can fire action potentials during precise intervals within a behavioral task. The intervals can last as little as a fraction of a second; it is possible that specific brain regions or neurons are required only at specific times in a task, not continuously. In humans, use of transcranial magnetic stimulation to disrupt the visual cortex has demonstrated that conscious perception requires intact cortical performance during temporal windows that last tens of milliseconds, occurring at precise times after visual stimulus presentation. Accordingly, a method for disrupting activity in targeted cell types for very precisely delimited periods of time (e.g., several milliseconds) could help answer a number of outstanding questions, and enable novel ones to be asked. For example, one question involves the identification of the precise brain regions, cell types, and activity patterns required at each phase (sensory, decision-making and motor) of a behavioral task. Another question involves, for a particular perception (e.g., feeling, decision, memory, or action) identifying the precise number of neurons that must be active within a certain region and how long the neurons are active. Another question involves the identification of the causal role of neural synchrony and precise spike timing in neural computation, plasticity, and pathological brain function. As memories are encoded, consolidated, and forgotten, it can be important to identifying how the critical neural loci of memory changes.